Popping vitamin D pills won’t protect you against COVID, according to new research. A large-scale study shows no evidence that taking the vitamin reduces infection rates or severity of the disease.

Vitamin D was believed to slash deaths by 60 percent, sparking calls for it to be given to hospital patients. Those receiving the supplements, according to earlier reports, were found to be 80 percent less likely to be admitted to ICU. Now an analysis of almost 1.3 million people has shown people with high vitamin D levels are just as prone to the coronavirus as everyone else.

They were identified through a technique called “Mendelian randomization,” which uses genetic variants linked to a potential risk factor. Study participants were drawn from eleven countries across Europe.

“In the past, Mendelian randomization has consistently predicted results of large, expensive, and timely vitamin D trials,” explains study lead author Dr. Guillaume Butler-Laporte of McGill University, in a statement. “Here, this method does not show clear evidence vitamin D supplementation would have a large effect on COVID-19 outcomes.”

A host of previous studies have suggested that severely ill patients deficient in the nutrient are more likely to die. One study claimed 99 percent of vitamin D deficient patients succumbed to COVID in a hospital in Indonesia, compared to only four percent of those with healthy vitamin D levels.

But the Canadian team says these studies were observational and may have failed to take into account other factors. The latest findings, published in the journal PLOS Medicine and based on genetic data, do not support the theory.

Dr. Butler-Laporte and colleagues analyzed genetic variants of 4,134 infected and 1,284,876 non-infected individuals. Predisposition for high amounts of vitamin D was not associated with less severe disease outcomes.

“The ability of vitamin D to protect against severe COVID-19 illness is of great interest to public health experts, but has limited supporting evidence. Raising circulating vitamin D levels through supplementation may not improve COVID-19 outcomes in the general population,” Dr. Butler-Laporte says. “Vitamin D supplementation as a public health measure to improve outcomes is not supported by this study. Most importantly, our results suggest investment in other therapeutic or preventative avenues should be prioritized for COVID-19 randomized clinical trials.

“Most vitamin D studies are very difficult to interpret since they cannot adjust for the known risk factors for severe COVID-19. These include older age, institutionalization, and having chronic diseases, which are also predictors of low vitamin D. Therefore, the best way to answer the question of the effect of vitamin D would be through randomized trials,” he continues. “But these are complex and resource-intensive, and take a long time during a pandemic. Mendelian randomization can provide more clear insights into the role of risk factors like vitamin D because they can decrease potential bias from associated risk factors like institutionalization and chronic disease.”

The researchers point out that individuals with vitamin D deficiency were not included in the study. It remains possible the supplements may protect truly deficient patients against COVID-19.

Future studies will also be needed to determine the relationship in populations of non-European ancestry. Some scientists have suggested darker-skinned people are more likely to die of COVID-19 because they are more likely to be vitamin D deficient.